The present invention relates to an image processing system for detecting a ground level from an image data density to remove thereof.
In the image recording apparatus such as the copying machine, the facsimile, etc., not only the manuscript using the ordinary white paper but also the manuscript using various papers such as the recycled paper, the colored paper, etc. is used as the object of reading. In this manner, since the ground density is high in the manuscript using the paper other than the ordinary paper, the ground of the manuscript appears in the output image to result in the dirty image if the image data that arc read by the manuscript reading portion such as the CCD sensor, or the like are output as they are.
Therefore, in the prior art, the process of executing the developing bias adjustment by reading a particular area near the center of the manuscript to detect the average quantity of light is applied to such manuscript the ground of which has a certain density.
Also, in the Unexamined Japanese Patent Application Publication No. Hei 4-37259, the technology that the threshold value for the ground removal can be set every area of the image data and also the threshold value can be switched by detecting respective ground density areas from the manuscript in which a plurality of ground densities are mixedly present is disclosed.
In addition, in the Unexamined Japanese Patent Application Publication No.Hei 4-37258, the technology that the optimum threshold value for the ground removal can be decided by detecting precisely respective ground density areas from the pasted manuscript in which a plurality of ground densities are mixedly present is disclosed.
However, the abrupt change in the ground level is caused at the border portion of the image in the pasted manuscript, otherwise the manuscript having the unevenness in the ground, except the pasted manuscript, such that the change in the ground level is continued successively appears similarly as the change in the ground level. Therefore, if the ground level switching like the technology disclosed in the Unexamined Japanese Patent Application Publication No. Hei 4-37259 is applied to the manuscript having the ground unevenness, there is caused the problem that the unevenness still remains in the area, at which the ground level is switched, of the image after the ground is removed.
Also, since both the pasted manuscript and the manuscript having the ground unevenness have the change in the ground level, it is difficult to discriminate them. If the manuscript having the ground unevenness is contained in the pasted manuscript, it is difficult to execute the process such that the switching process is not applied to the image having the unevenness, or the like.
In addition, if the image such as the photographic image, the ground level of which is not constant, is contained in the pasted manuscript, it is difficult to discriminate such image from the manuscript having the ground unevenness. Thus, it is impossible not to apply the ground removing process to the photographic image.
Further, in the case of the manuscript having the ground unevenness, sometimes difference between the calculated ground level and the ground level of the neighboring pixels or areas occurs and then remains as the unevenness in the image from which the ground is removed.
In addition, in some cases the images having various ground levels are contained in the pasted manuscript. Thus, if the ground level becomes higher, difference between the necessary density of letters, lines, etc. and the ground density becomes close to each other to result in the low contrast. Therefore, there is caused the problem that, if the image has the higher ground level, the necessary densities disappear by the ground removing process, or the densities become light.